Our invention relates to a rock splitter, that is, an apparatus for splitting or fracturing rock, concrete structures, etc., by being inserted into a drill hole created therein. The rock splitter in accordance with our invention is of the type having a wedge driven by a hydraulic cylinder or like actuator.
Several problems have been attendant upon rock splitters of the class under consideration. One is the difficulty of insertion of a rock splitter to a required depth in a drill hole formed in rock to be fractured. The difficulty arises because the drill hole is not exactly cylindrical but usually has bends and irregularities of the wall surface. Consequently, even if smaller in width than the nominal diameter of the drill hole, the wedge assembly of the rock splitter has been easy to jam in the hole before full insertion therein.
A conventional measure to counter this problem has been to make the pair of wedge guides of the wedge assembly, slidably holding the wedge therebetween, considerably thicker at their forward or lower end portions, and to drill holes of correspondingly large diameter in rock to be split. This known solution is subject to the objection that the clearance between the slender portion of the wedge assembly and the wall surface of the drill hole serves no useful purpose in splitting the rock. Also, since the wedge assembly makes direct contact with the rock only at its thick end portion, the reactive forces of the rock concentrate at this portion, giving rise to the possibility of seizure of the wedge between the guides through excessive pressure and friction. Further the slender portion of the wedge assembly has been easy to become distorted by stresses exerted thereon during the thrust of the wedge. Still further the strength of the slender portion of the wedge assembly sets a limit on the force with which the hydraulic cylinderthrusts down the wedge. An additional drawback is that the prior art rock splitter becomes totally unusable in the event of lessening of the drill hole diameter through wear of the drill bit, unless the bit is replaced.
Another problem with the prior art concerns the splitting of large rock or the like. Most rock splitters available today, for use in drill holes ranging from 40 to 60 millimeters in diameter, can create a rupture having a maximum width of 15 to 20 millimeters, with one thrust of the wedge. This is insufficient for thoroughly splitting extremely large rocks or thick rock formations. The usual practice in such cases is to withdraw the rock splitter out of the drill hole after the initial thrust of the wedge and to replace the wedge guides with thicker ones or to insert spacers in the wedge assembly. Then the splitter is reinserted in the drill hole, whose diameter has been increased by the initial thrust of the wedge, to repeat the wedging operation.
This conventional practice is objectionable in view of the time-consuming and troublesome operation of wedge guide replacement or spacer insertion. Moreover, having been broken loose by the initial thrust of the wedge, the wall of the drill hole more or less crumbles during the withdrawal and reinsertion of the rock splitter. The consequent increase in the diameter of the drill hole makes the subsequent wedging operation materially less effective in spite of the use of thicker wedge guides or of spacers.
As an alternative to the above conventional practice it may be contemplated to increase the stroke of the wedge. This solution is impractical, or at least highly uneconomical, because of the need for the use of a hydraulic cylinder of correspondingly long piston stroke and for the drilling of correspondingly deep holes.
A further problem with the conventional rock splitters pertains to the diameter of drill holes to be formed in rock for receiving them. If the wedging force of the prior art devices is to be increased for more efficient splitting operation, their wedge assemblies must be made larger in cross sectional size to gain strength for withstanding the increased force. The larger wedge assemblies require, of course, correspondingly large drill holes. However, the greater the diameter of drill holes, the longer time and the more expensive equipment are needed to create them.